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  <div class="section" id="module-imp">
<span id="imp-access-the-import-internals"></span><h1>36.2. <a class="reference internal" href="#module-imp" title="imp: Access the implementation of the import statement. (已移除)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">imp</span></code></a> --- Access the <a class="reference internal" href="../reference/import.html#importsystem"><span class="std std-ref">import</span></a> internals<a class="headerlink" href="#module-imp" title="永久链接至标题">¶</a></h1>
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.6/Lib/imp.py">Lib/imp.py</a></p>
<div class="deprecated">
<p><span class="versionmodified">3.4 版后已移除: </span>The <a class="reference internal" href="#module-imp" title="imp: Access the implementation of the import statement. (已移除)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">imp</span></code></a> package is pending deprecation in favor of <a class="reference internal" href="importlib.html#module-importlib" title="importlib: The implementation of the import machinery."><code class="xref py py-mod docutils literal notranslate"><span class="pre">importlib</span></code></a>.</p>
</div>
<hr class="docutils" id="index-0" />
<p>This module provides an interface to the mechanisms used to implement the
<a class="reference internal" href="../reference/simple_stmts.html#import"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">import</span></code></a> statement.  It defines the following constants and functions:</p>
<dl class="function">
<dt id="imp.get_magic">
<code class="descclassname">imp.</code><code class="descname">get_magic</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#imp.get_magic" title="永久链接至目标">¶</a></dt>
<dd><p id="index-1">Return the magic string value used to recognize byte-compiled code files
(<code class="file docutils literal notranslate"><span class="pre">.pyc</span></code> files).  (This value may be different for each Python version.)</p>
<div class="deprecated">
<p><span class="versionmodified">3.4 版后已移除: </span>Use <a class="reference internal" href="importlib.html#importlib.util.MAGIC_NUMBER" title="importlib.util.MAGIC_NUMBER"><code class="xref py py-attr docutils literal notranslate"><span class="pre">importlib.util.MAGIC_NUMBER</span></code></a> instead.</p>
</div>
</dd></dl>

<dl class="function">
<dt id="imp.get_suffixes">
<code class="descclassname">imp.</code><code class="descname">get_suffixes</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#imp.get_suffixes" title="永久链接至目标">¶</a></dt>
<dd><p>Return a list of 3-element tuples, each describing a particular type of
module. Each triple has the form <code class="docutils literal notranslate"><span class="pre">(suffix,</span> <span class="pre">mode,</span> <span class="pre">type)</span></code>, where <em>suffix</em> is
a string to be appended to the module name to form the filename to search
for, <em>mode</em> is the mode string to pass to the built-in <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a> function
to open the file (this can be <code class="docutils literal notranslate"><span class="pre">'r'</span></code> for text files or <code class="docutils literal notranslate"><span class="pre">'rb'</span></code> for binary
files), and <em>type</em> is the file type, which has one of the values
<a class="reference internal" href="#imp.PY_SOURCE" title="imp.PY_SOURCE"><code class="xref py py-const docutils literal notranslate"><span class="pre">PY_SOURCE</span></code></a>, <a class="reference internal" href="#imp.PY_COMPILED" title="imp.PY_COMPILED"><code class="xref py py-const docutils literal notranslate"><span class="pre">PY_COMPILED</span></code></a>, or <a class="reference internal" href="#imp.C_EXTENSION" title="imp.C_EXTENSION"><code class="xref py py-const docutils literal notranslate"><span class="pre">C_EXTENSION</span></code></a>, described
below.</p>
<div class="deprecated">
<p><span class="versionmodified">3.3 版后已移除: </span>Use the constants defined on <a class="reference internal" href="importlib.html#module-importlib.machinery" title="importlib.machinery: Importers and path hooks"><code class="xref py py-mod docutils literal notranslate"><span class="pre">importlib.machinery</span></code></a> instead.</p>
</div>
</dd></dl>

<dl class="function">
<dt id="imp.find_module">
<code class="descclassname">imp.</code><code class="descname">find_module</code><span class="sig-paren">(</span><em>name</em><span class="optional">[</span>, <em>path</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#imp.find_module" title="永久链接至目标">¶</a></dt>
<dd><p>Try to find the module <em>name</em>.  If <em>path</em> is omitted or <code class="docutils literal notranslate"><span class="pre">None</span></code>, the list of
directory names given by <code class="docutils literal notranslate"><span class="pre">sys.path</span></code> is searched, but first a few special
places are searched: the function tries to find a built-in module with the
given name (<a class="reference internal" href="#imp.C_BUILTIN" title="imp.C_BUILTIN"><code class="xref py py-const docutils literal notranslate"><span class="pre">C_BUILTIN</span></code></a>), then a frozen module (<a class="reference internal" href="#imp.PY_FROZEN" title="imp.PY_FROZEN"><code class="xref py py-const docutils literal notranslate"><span class="pre">PY_FROZEN</span></code></a>),
and on some systems some other places are looked in as well (on Windows, it
looks in the registry which may point to a specific file).</p>
<p>Otherwise, <em>path</em> must be a list of directory names; each directory is
searched for files with any of the suffixes returned by <a class="reference internal" href="#imp.get_suffixes" title="imp.get_suffixes"><code class="xref py py-func docutils literal notranslate"><span class="pre">get_suffixes()</span></code></a>
above.  Invalid names in the list are silently ignored (but all list items
must be strings).</p>
<p>If search is successful, the return value is a 3-element tuple <code class="docutils literal notranslate"><span class="pre">(file,</span>
<span class="pre">pathname,</span> <span class="pre">description)</span></code>:</p>
<p><em>file</em> is an open <a class="reference internal" href="../glossary.html#term-file-object"><span class="xref std std-term">file object</span></a> positioned at the beginning, <em>pathname</em>
is the pathname of the file found, and <em>description</em> is a 3-element tuple as
contained in the list returned by <a class="reference internal" href="#imp.get_suffixes" title="imp.get_suffixes"><code class="xref py py-func docutils literal notranslate"><span class="pre">get_suffixes()</span></code></a> describing the kind of
module found.</p>
<p>If the module does not live in a file, the returned <em>file</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code>,
<em>pathname</em> is the empty string, and the <em>description</em> tuple contains empty
strings for its suffix and mode; the module type is indicated as given in
parentheses above.  If the search is unsuccessful, <a class="reference internal" href="exceptions.html#ImportError" title="ImportError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ImportError</span></code></a> is
raised.  Other exceptions indicate problems with the arguments or
environment.</p>
<p>If the module is a package, <em>file</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code>, <em>pathname</em> is the package
path and the last item in the <em>description</em> tuple is <a class="reference internal" href="#imp.PKG_DIRECTORY" title="imp.PKG_DIRECTORY"><code class="xref py py-const docutils literal notranslate"><span class="pre">PKG_DIRECTORY</span></code></a>.</p>
<p>This function does not handle hierarchical module names (names containing
dots).  In order to find <em>P.M</em>, that is, submodule <em>M</em> of package <em>P</em>, use
<a class="reference internal" href="#imp.find_module" title="imp.find_module"><code class="xref py py-func docutils literal notranslate"><span class="pre">find_module()</span></code></a> and <a class="reference internal" href="#imp.load_module" title="imp.load_module"><code class="xref py py-func docutils literal notranslate"><span class="pre">load_module()</span></code></a> to find and load package <em>P</em>, and
then use <a class="reference internal" href="#imp.find_module" title="imp.find_module"><code class="xref py py-func docutils literal notranslate"><span class="pre">find_module()</span></code></a> with the <em>path</em> argument set to <code class="docutils literal notranslate"><span class="pre">P.__path__</span></code>.
When <em>P</em> itself has a dotted name, apply this recipe recursively.</p>
<div class="deprecated">
<p><span class="versionmodified">3.3 版后已移除: </span>Use <a class="reference internal" href="importlib.html#importlib.util.find_spec" title="importlib.util.find_spec"><code class="xref py py-func docutils literal notranslate"><span class="pre">importlib.util.find_spec()</span></code></a> instead unless Python 3.3
compatibility is required, in which case use
<a class="reference internal" href="importlib.html#importlib.find_loader" title="importlib.find_loader"><code class="xref py py-func docutils literal notranslate"><span class="pre">importlib.find_loader()</span></code></a>. For example usage of the former case,
see the <a class="reference internal" href="importlib.html#importlib-examples"><span class="std std-ref">Examples</span></a> section of the <a class="reference internal" href="importlib.html#module-importlib" title="importlib: The implementation of the import machinery."><code class="xref py py-mod docutils literal notranslate"><span class="pre">importlib</span></code></a>
documentation.</p>
</div>
</dd></dl>

<dl class="function">
<dt id="imp.load_module">
<code class="descclassname">imp.</code><code class="descname">load_module</code><span class="sig-paren">(</span><em>name</em>, <em>file</em>, <em>pathname</em>, <em>description</em><span class="sig-paren">)</span><a class="headerlink" href="#imp.load_module" title="永久链接至目标">¶</a></dt>
<dd><p>Load a module that was previously found by <a class="reference internal" href="#imp.find_module" title="imp.find_module"><code class="xref py py-func docutils literal notranslate"><span class="pre">find_module()</span></code></a> (or by an
otherwise conducted search yielding compatible results).  This function does
more than importing the module: if the module was already imported, it will
reload the module!  The <em>name</em> argument indicates the full
module name (including the package name, if this is a submodule of a
package).  The <em>file</em> argument is an open file, and <em>pathname</em> is the
corresponding file name; these can be <code class="docutils literal notranslate"><span class="pre">None</span></code> and <code class="docutils literal notranslate"><span class="pre">''</span></code>, respectively, when
the module is a package or not being loaded from a file.  The <em>description</em>
argument is a tuple, as would be returned by <a class="reference internal" href="#imp.get_suffixes" title="imp.get_suffixes"><code class="xref py py-func docutils literal notranslate"><span class="pre">get_suffixes()</span></code></a>, describing
what kind of module must be loaded.</p>
<p>If the load is successful, the return value is the module object; otherwise,
an exception (usually <a class="reference internal" href="exceptions.html#ImportError" title="ImportError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ImportError</span></code></a>) is raised.</p>
<p><strong>Important:</strong> the caller is responsible for closing the <em>file</em> argument, if
it was not <code class="docutils literal notranslate"><span class="pre">None</span></code>, even when an exception is raised.  This is best done
using a <a class="reference internal" href="../reference/compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">try</span></code></a> ... <a class="reference internal" href="../reference/compound_stmts.html#finally"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">finally</span></code></a> statement.</p>
<div class="deprecated">
<p><span class="versionmodified">3.3 版后已移除: </span>If previously used in conjunction with <a class="reference internal" href="#imp.find_module" title="imp.find_module"><code class="xref py py-func docutils literal notranslate"><span class="pre">imp.find_module()</span></code></a> then
consider using <a class="reference internal" href="importlib.html#importlib.import_module" title="importlib.import_module"><code class="xref py py-func docutils literal notranslate"><span class="pre">importlib.import_module()</span></code></a>, otherwise use the loader
returned by the replacement you chose for <a class="reference internal" href="#imp.find_module" title="imp.find_module"><code class="xref py py-func docutils literal notranslate"><span class="pre">imp.find_module()</span></code></a>. If you
called <a class="reference internal" href="#imp.load_module" title="imp.load_module"><code class="xref py py-func docutils literal notranslate"><span class="pre">imp.load_module()</span></code></a> and related functions directly with file
path arguments then use a combination of
<a class="reference internal" href="importlib.html#importlib.util.spec_from_file_location" title="importlib.util.spec_from_file_location"><code class="xref py py-func docutils literal notranslate"><span class="pre">importlib.util.spec_from_file_location()</span></code></a> and
<a class="reference internal" href="importlib.html#importlib.util.module_from_spec" title="importlib.util.module_from_spec"><code class="xref py py-func docutils literal notranslate"><span class="pre">importlib.util.module_from_spec()</span></code></a>. See the <a class="reference internal" href="importlib.html#importlib-examples"><span class="std std-ref">Examples</span></a>
section of the <a class="reference internal" href="importlib.html#module-importlib" title="importlib: The implementation of the import machinery."><code class="xref py py-mod docutils literal notranslate"><span class="pre">importlib</span></code></a> documentation for details of the various
approaches.</p>
</div>
</dd></dl>

<dl class="function">
<dt id="imp.new_module">
<code class="descclassname">imp.</code><code class="descname">new_module</code><span class="sig-paren">(</span><em>name</em><span class="sig-paren">)</span><a class="headerlink" href="#imp.new_module" title="永久链接至目标">¶</a></dt>
<dd><p>Return a new empty module object called <em>name</em>.  This object is <em>not</em> inserted
in <code class="docutils literal notranslate"><span class="pre">sys.modules</span></code>.</p>
<div class="deprecated">
<p><span class="versionmodified">3.4 版后已移除: </span>Use <a class="reference internal" href="importlib.html#importlib.util.module_from_spec" title="importlib.util.module_from_spec"><code class="xref py py-func docutils literal notranslate"><span class="pre">importlib.util.module_from_spec()</span></code></a> instead.</p>
</div>
</dd></dl>

<dl class="function">
<dt id="imp.reload">
<code class="descclassname">imp.</code><code class="descname">reload</code><span class="sig-paren">(</span><em>module</em><span class="sig-paren">)</span><a class="headerlink" href="#imp.reload" title="永久链接至目标">¶</a></dt>
<dd><p>Reload a previously imported <em>module</em>.  The argument must be a module object, so
it must have been successfully imported before.  This is useful if you have
edited the module source file using an external editor and want to try out the
new version without leaving the Python interpreter.  The return value is the
module object (the same as the <em>module</em> argument).</p>
<p>When <code class="docutils literal notranslate"><span class="pre">reload(module)</span></code> is executed:</p>
<ul class="simple">
<li>Python modules' code is recompiled and the module-level code reexecuted,
defining a new set of objects which are bound to names in the module's
dictionary.  The <code class="docutils literal notranslate"><span class="pre">init</span></code> function of extension modules is not called a second
time.</li>
<li>As with all other objects in Python the old objects are only reclaimed after
their reference counts drop to zero.</li>
<li>The names in the module namespace are updated to point to any new or changed
objects.</li>
<li>Other references to the old objects (such as names external to the module) are
not rebound to refer to the new objects and must be updated in each namespace
where they occur if that is desired.</li>
</ul>
<p>There are a number of other caveats:</p>
<p>When a module is reloaded, its dictionary (containing the module's global
variables) is retained.  Redefinitions of names will override the old
definitions, so this is generally not a problem.  If the new version of a module
does not define a name that was defined by the old version, the old definition
remains.  This feature can be used to the module's advantage if it maintains a
global table or cache of objects --- with a <a class="reference internal" href="../reference/compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">try</span></code></a> statement it can test
for the table's presence and skip its initialization if desired:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">try</span><span class="p">:</span>
    <span class="n">cache</span>
<span class="k">except</span> <span class="ne">NameError</span><span class="p">:</span>
    <span class="n">cache</span> <span class="o">=</span> <span class="p">{}</span>
</pre></div>
</div>
<p>It is legal though generally not very useful to reload built-in or dynamically
loaded modules, except for <a class="reference internal" href="sys.html#module-sys" title="sys: Access system-specific parameters and functions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">sys</span></code></a>, <a class="reference internal" href="__main__.html#module-__main__" title="__main__: The environment where the top-level script is run."><code class="xref py py-mod docutils literal notranslate"><span class="pre">__main__</span></code></a> and <a class="reference internal" href="builtins.html#module-builtins" title="builtins: The module that provides the built-in namespace."><code class="xref py py-mod docutils literal notranslate"><span class="pre">builtins</span></code></a>.
In many cases, however, extension modules are not designed to be initialized
more than once, and may fail in arbitrary ways when reloaded.</p>
<p>If a module imports objects from another module using <a class="reference internal" href="../reference/simple_stmts.html#from"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">from</span></code></a> ...
<a class="reference internal" href="../reference/simple_stmts.html#import"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">import</span></code></a> ..., calling <a class="reference internal" href="#imp.reload" title="imp.reload"><code class="xref py py-func docutils literal notranslate"><span class="pre">reload()</span></code></a> for the other module does not
redefine the objects imported from it --- one way around this is to re-execute
the <a class="reference internal" href="../reference/simple_stmts.html#from"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">from</span></code></a> statement, another is to use <a class="reference internal" href="../reference/simple_stmts.html#import"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">import</span></code></a> and qualified
names (<em>module</em>.*name*) instead.</p>
<p>If a module instantiates instances of a class, reloading the module that defines
the class does not affect the method definitions of the instances --- they
continue to use the old class definition.  The same is true for derived classes.</p>
<div class="versionchanged">
<p><span class="versionmodified">在 3.3 版更改: </span>Relies on both <code class="docutils literal notranslate"><span class="pre">__name__</span></code> and <code class="docutils literal notranslate"><span class="pre">__loader__</span></code> being defined on the module
being reloaded instead of just <code class="docutils literal notranslate"><span class="pre">__name__</span></code>.</p>
</div>
<div class="deprecated">
<p><span class="versionmodified">3.4 版后已移除: </span>Use <a class="reference internal" href="importlib.html#importlib.reload" title="importlib.reload"><code class="xref py py-func docutils literal notranslate"><span class="pre">importlib.reload()</span></code></a> instead.</p>
</div>
</dd></dl>

<p>The following functions are conveniences for handling <span class="target" id="index-2"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3147"><strong>PEP 3147</strong></a> byte-compiled
file paths.</p>
<div class="versionadded">
<p><span class="versionmodified">3.2 新版功能.</span></p>
</div>
<dl class="function">
<dt id="imp.cache_from_source">
<code class="descclassname">imp.</code><code class="descname">cache_from_source</code><span class="sig-paren">(</span><em>path</em>, <em>debug_override=None</em><span class="sig-paren">)</span><a class="headerlink" href="#imp.cache_from_source" title="永久链接至目标">¶</a></dt>
<dd><p>Return the <span class="target" id="index-3"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3147"><strong>PEP 3147</strong></a> path to the byte-compiled file associated with the
source <em>path</em>.  For example, if <em>path</em> is <code class="docutils literal notranslate"><span class="pre">/foo/bar/baz.py</span></code> the return
value would be <code class="docutils literal notranslate"><span class="pre">/foo/bar/__pycache__/baz.cpython-32.pyc</span></code> for Python 3.2.
The <code class="docutils literal notranslate"><span class="pre">cpython-32</span></code> string comes from the current magic tag (see
<a class="reference internal" href="#imp.get_tag" title="imp.get_tag"><code class="xref py py-func docutils literal notranslate"><span class="pre">get_tag()</span></code></a>; if <code class="xref py py-attr docutils literal notranslate"><span class="pre">sys.implementation.cache_tag</span></code> is not defined then
<a class="reference internal" href="exceptions.html#NotImplementedError" title="NotImplementedError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">NotImplementedError</span></code></a> will be raised). By passing in <code class="docutils literal notranslate"><span class="pre">True</span></code> or
<code class="docutils literal notranslate"><span class="pre">False</span></code> for <em>debug_override</em> you can override the system's value for
<code class="docutils literal notranslate"><span class="pre">__debug__</span></code>, leading to optimized bytecode.</p>
<p><em>path</em> need not exist.</p>
<div class="versionchanged">
<p><span class="versionmodified">在 3.3 版更改: </span>If <code class="xref py py-attr docutils literal notranslate"><span class="pre">sys.implementation.cache_tag</span></code> is <code class="docutils literal notranslate"><span class="pre">None</span></code>, then
<a class="reference internal" href="exceptions.html#NotImplementedError" title="NotImplementedError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">NotImplementedError</span></code></a> is raised.</p>
</div>
<div class="deprecated">
<p><span class="versionmodified">3.4 版后已移除: </span>Use <a class="reference internal" href="importlib.html#importlib.util.cache_from_source" title="importlib.util.cache_from_source"><code class="xref py py-func docutils literal notranslate"><span class="pre">importlib.util.cache_from_source()</span></code></a> instead.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">在 3.5 版更改: </span>The <em>debug_override</em> parameter no longer creates a <code class="docutils literal notranslate"><span class="pre">.pyo</span></code> file.</p>
</div>
</dd></dl>

<dl class="function">
<dt id="imp.source_from_cache">
<code class="descclassname">imp.</code><code class="descname">source_from_cache</code><span class="sig-paren">(</span><em>path</em><span class="sig-paren">)</span><a class="headerlink" href="#imp.source_from_cache" title="永久链接至目标">¶</a></dt>
<dd><p>Given the <em>path</em> to a <span class="target" id="index-4"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3147"><strong>PEP 3147</strong></a> file name, return the associated source code
file path.  For example, if <em>path</em> is
<code class="docutils literal notranslate"><span class="pre">/foo/bar/__pycache__/baz.cpython-32.pyc</span></code> the returned path would be
<code class="docutils literal notranslate"><span class="pre">/foo/bar/baz.py</span></code>.  <em>path</em> need not exist, however if it does not conform
to <span class="target" id="index-5"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3147"><strong>PEP 3147</strong></a> format, a <code class="docutils literal notranslate"><span class="pre">ValueError</span></code> is raised. If
<code class="xref py py-attr docutils literal notranslate"><span class="pre">sys.implementation.cache_tag</span></code> is not defined,
<a class="reference internal" href="exceptions.html#NotImplementedError" title="NotImplementedError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">NotImplementedError</span></code></a> is raised.</p>
<div class="versionchanged">
<p><span class="versionmodified">在 3.3 版更改: </span>Raise <a class="reference internal" href="exceptions.html#NotImplementedError" title="NotImplementedError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">NotImplementedError</span></code></a> when
<code class="xref py py-attr docutils literal notranslate"><span class="pre">sys.implementation.cache_tag</span></code> is not defined.</p>
</div>
<div class="deprecated">
<p><span class="versionmodified">3.4 版后已移除: </span>Use <a class="reference internal" href="importlib.html#importlib.util.source_from_cache" title="importlib.util.source_from_cache"><code class="xref py py-func docutils literal notranslate"><span class="pre">importlib.util.source_from_cache()</span></code></a> instead.</p>
</div>
</dd></dl>

<dl class="function">
<dt id="imp.get_tag">
<code class="descclassname">imp.</code><code class="descname">get_tag</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#imp.get_tag" title="永久链接至目标">¶</a></dt>
<dd><p>Return the <span class="target" id="index-6"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3147"><strong>PEP 3147</strong></a> magic tag string matching this version of Python's
magic number, as returned by <a class="reference internal" href="#imp.get_magic" title="imp.get_magic"><code class="xref py py-func docutils literal notranslate"><span class="pre">get_magic()</span></code></a>.</p>
<div class="deprecated">
<p><span class="versionmodified">3.4 版后已移除: </span>Use <code class="xref py py-attr docutils literal notranslate"><span class="pre">sys.implementation.cache_tag</span></code> directly starting
in Python 3.3.</p>
</div>
</dd></dl>

<p>The following functions help interact with the import system's internal
locking mechanism.  Locking semantics of imports are an implementation
detail which may vary from release to release.  However, Python ensures
that circular imports work without any deadlocks.</p>
<dl class="function">
<dt id="imp.lock_held">
<code class="descclassname">imp.</code><code class="descname">lock_held</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#imp.lock_held" title="永久链接至目标">¶</a></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the global import lock is currently held, else
<code class="docutils literal notranslate"><span class="pre">False</span></code>. On platforms without threads, always return <code class="docutils literal notranslate"><span class="pre">False</span></code>.</p>
<p>On platforms with threads, a thread executing an import first holds a
global import lock, then sets up a per-module lock for the rest of the
import.  This blocks other threads from importing the same module until
the original import completes, preventing other threads from seeing
incomplete module objects constructed by the original thread.  An
exception is made for circular imports, which by construction have to
expose an incomplete module object at some point.</p>
<div class="versionchanged">
<p><span class="versionmodified">在 3.3 版更改: </span>The locking scheme has changed to per-module locks for
the most part.  A global import lock is kept for some critical tasks,
such as initializing the per-module locks.</p>
</div>
<div class="deprecated">
<p><span class="versionmodified">3.4 版后已移除.</span></p>
</div>
</dd></dl>

<dl class="function">
<dt id="imp.acquire_lock">
<code class="descclassname">imp.</code><code class="descname">acquire_lock</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#imp.acquire_lock" title="永久链接至目标">¶</a></dt>
<dd><p>Acquire the interpreter's global import lock for the current thread.
This lock should be used by import hooks to ensure thread-safety when
importing modules.</p>
<p>Once a thread has acquired the import lock, the same thread may acquire it
again without blocking; the thread must release it once for each time it has
acquired it.</p>
<p>On platforms without threads, this function does nothing.</p>
<div class="versionchanged">
<p><span class="versionmodified">在 3.3 版更改: </span>The locking scheme has changed to per-module locks for
the most part.  A global import lock is kept for some critical tasks,
such as initializing the per-module locks.</p>
</div>
<div class="deprecated">
<p><span class="versionmodified">3.4 版后已移除.</span></p>
</div>
</dd></dl>

<dl class="function">
<dt id="imp.release_lock">
<code class="descclassname">imp.</code><code class="descname">release_lock</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#imp.release_lock" title="永久链接至目标">¶</a></dt>
<dd><p>Release the interpreter's global import lock. On platforms without
threads, this function does nothing.</p>
<div class="versionchanged">
<p><span class="versionmodified">在 3.3 版更改: </span>The locking scheme has changed to per-module locks for
the most part.  A global import lock is kept for some critical tasks,
such as initializing the per-module locks.</p>
</div>
<div class="deprecated">
<p><span class="versionmodified">3.4 版后已移除.</span></p>
</div>
</dd></dl>

<p>The following constants with integer values, defined in this module, are used
to indicate the search result of <a class="reference internal" href="#imp.find_module" title="imp.find_module"><code class="xref py py-func docutils literal notranslate"><span class="pre">find_module()</span></code></a>.</p>
<dl class="data">
<dt id="imp.PY_SOURCE">
<code class="descclassname">imp.</code><code class="descname">PY_SOURCE</code><a class="headerlink" href="#imp.PY_SOURCE" title="永久链接至目标">¶</a></dt>
<dd><p>The module was found as a source file.</p>
<div class="deprecated">
<p><span class="versionmodified">3.3 版后已移除.</span></p>
</div>
</dd></dl>

<dl class="data">
<dt id="imp.PY_COMPILED">
<code class="descclassname">imp.</code><code class="descname">PY_COMPILED</code><a class="headerlink" href="#imp.PY_COMPILED" title="永久链接至目标">¶</a></dt>
<dd><p>The module was found as a compiled code object file.</p>
<div class="deprecated">
<p><span class="versionmodified">3.3 版后已移除.</span></p>
</div>
</dd></dl>

<dl class="data">
<dt id="imp.C_EXTENSION">
<code class="descclassname">imp.</code><code class="descname">C_EXTENSION</code><a class="headerlink" href="#imp.C_EXTENSION" title="永久链接至目标">¶</a></dt>
<dd><p>The module was found as dynamically loadable shared library.</p>
<div class="deprecated">
<p><span class="versionmodified">3.3 版后已移除.</span></p>
</div>
</dd></dl>

<dl class="data">
<dt id="imp.PKG_DIRECTORY">
<code class="descclassname">imp.</code><code class="descname">PKG_DIRECTORY</code><a class="headerlink" href="#imp.PKG_DIRECTORY" title="永久链接至目标">¶</a></dt>
<dd><p>The module was found as a package directory.</p>
<div class="deprecated">
<p><span class="versionmodified">3.3 版后已移除.</span></p>
</div>
</dd></dl>

<dl class="data">
<dt id="imp.C_BUILTIN">
<code class="descclassname">imp.</code><code class="descname">C_BUILTIN</code><a class="headerlink" href="#imp.C_BUILTIN" title="永久链接至目标">¶</a></dt>
<dd><p>The module was found as a built-in module.</p>
<div class="deprecated">
<p><span class="versionmodified">3.3 版后已移除.</span></p>
</div>
</dd></dl>

<dl class="data">
<dt id="imp.PY_FROZEN">
<code class="descclassname">imp.</code><code class="descname">PY_FROZEN</code><a class="headerlink" href="#imp.PY_FROZEN" title="永久链接至目标">¶</a></dt>
<dd><p>The module was found as a frozen module.</p>
<div class="deprecated">
<p><span class="versionmodified">3.3 版后已移除.</span></p>
</div>
</dd></dl>

<dl class="class">
<dt id="imp.NullImporter">
<em class="property">class </em><code class="descclassname">imp.</code><code class="descname">NullImporter</code><span class="sig-paren">(</span><em>path_string</em><span class="sig-paren">)</span><a class="headerlink" href="#imp.NullImporter" title="永久链接至目标">¶</a></dt>
<dd><p>The <a class="reference internal" href="#imp.NullImporter" title="imp.NullImporter"><code class="xref py py-class docutils literal notranslate"><span class="pre">NullImporter</span></code></a> type is a <span class="target" id="index-7"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0302"><strong>PEP 302</strong></a> import hook that handles
non-directory path strings by failing to find any modules.  Calling this type
with an existing directory or empty string raises <a class="reference internal" href="exceptions.html#ImportError" title="ImportError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ImportError</span></code></a>.
Otherwise, a <a class="reference internal" href="#imp.NullImporter" title="imp.NullImporter"><code class="xref py py-class docutils literal notranslate"><span class="pre">NullImporter</span></code></a> instance is returned.</p>
<p>Instances have only one method:</p>
<dl class="method">
<dt id="imp.NullImporter.find_module">
<code class="descname">find_module</code><span class="sig-paren">(</span><em>fullname</em><span class="optional">[</span>, <em>path</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#imp.NullImporter.find_module" title="永久链接至目标">¶</a></dt>
<dd><p>This method always returns <code class="docutils literal notranslate"><span class="pre">None</span></code>, indicating that the requested module could
not be found.</p>
</dd></dl>

<div class="versionchanged">
<p><span class="versionmodified">在 3.3 版更改: </span><code class="docutils literal notranslate"><span class="pre">None</span></code> is inserted into <code class="docutils literal notranslate"><span class="pre">sys.path_importer_cache</span></code> instead of an
instance of <a class="reference internal" href="#imp.NullImporter" title="imp.NullImporter"><code class="xref py py-class docutils literal notranslate"><span class="pre">NullImporter</span></code></a>.</p>
</div>
<div class="deprecated">
<p><span class="versionmodified">3.4 版后已移除: </span>Insert <code class="docutils literal notranslate"><span class="pre">None</span></code> into <code class="docutils literal notranslate"><span class="pre">sys.path_importer_cache</span></code> instead.</p>
</div>
</dd></dl>

<div class="section" id="examples">
<span id="examples-imp"></span><h2>36.2.1. Examples<a class="headerlink" href="#examples" title="永久链接至标题">¶</a></h2>
<p>The following function emulates what was the standard import statement up to
Python 1.4 (no hierarchical module names).  (This <em>implementation</em> wouldn't work
in that version, since <a class="reference internal" href="#imp.find_module" title="imp.find_module"><code class="xref py py-func docutils literal notranslate"><span class="pre">find_module()</span></code></a> has been extended and
<a class="reference internal" href="#imp.load_module" title="imp.load_module"><code class="xref py py-func docutils literal notranslate"><span class="pre">load_module()</span></code></a> has been added in 1.4.)</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">imp</span>
<span class="kn">import</span> <span class="nn">sys</span>

<span class="k">def</span> <span class="nf">__import__</span><span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="nb">globals</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span> <span class="nb">locals</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span> <span class="n">fromlist</span><span class="o">=</span><span class="kc">None</span><span class="p">):</span>
    <span class="c1"># Fast path: see if the module has already been imported.</span>
    <span class="k">try</span><span class="p">:</span>
        <span class="k">return</span> <span class="n">sys</span><span class="o">.</span><span class="n">modules</span><span class="p">[</span><span class="n">name</span><span class="p">]</span>
    <span class="k">except</span> <span class="ne">KeyError</span><span class="p">:</span>
        <span class="k">pass</span>

    <span class="c1"># If any of the following calls raises an exception,</span>
    <span class="c1"># there&#39;s a problem we can&#39;t handle -- let the caller handle it.</span>

    <span class="n">fp</span><span class="p">,</span> <span class="n">pathname</span><span class="p">,</span> <span class="n">description</span> <span class="o">=</span> <span class="n">imp</span><span class="o">.</span><span class="n">find_module</span><span class="p">(</span><span class="n">name</span><span class="p">)</span>

    <span class="k">try</span><span class="p">:</span>
        <span class="k">return</span> <span class="n">imp</span><span class="o">.</span><span class="n">load_module</span><span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="n">fp</span><span class="p">,</span> <span class="n">pathname</span><span class="p">,</span> <span class="n">description</span><span class="p">)</span>
    <span class="k">finally</span><span class="p">:</span>
        <span class="c1"># Since we may exit via an exception, close fp explicitly.</span>
        <span class="k">if</span> <span class="n">fp</span><span class="p">:</span>
            <span class="n">fp</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
</div>
</div>


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<li><a class="reference internal" href="#">36.2. <code class="docutils literal notranslate"><span class="pre">imp</span></code> --- Access the <code class="docutils literal notranslate"><span class="pre">import</span></code> internals</a><ul>
<li><a class="reference internal" href="#examples">36.2.1. Examples</a></li>
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